It was Joaquin Phoenix’s first time. The chameleon-like actor with a penchant for the eccentric had never before debuted a movie in the snowy enclave of Sundance. While he roamed around the well-appointed Grey Goose suite on Main Street, admiring the rustic décor and the kettle of soup sitting on the bar top—not to mention the bartender, eager to serve whatever you like—Phoenix had to pause for a moment. “Look around. This is just fucking absurd,” he said. “Take a look around. Enjoy it.”

Phoenix was in Park City to promote his new movie, Don’t Worry, He Won’t Get Far On Foot, his first collaboration with director Gus Van Sant since the two worked together on 1995’s To Die For. (Amazon Studios will release the film theatrically on May 11.) Since then, Phoenix has been nominated for three Oscars, and Van Sant has directed a dozen movies. The two reunited to tell the long-gestating story of John Callahan, a quadriplegic cartoonist with tangerine-hued hair from Portland who won a huge following due to his very un-P.C. cartoon panels.

Van Sant has been working on the film for the past 20 years, first with Robin Williams in the lead, and now with the usually-brooding Phoenix, in what has to be the 43-year-old’s most joyous role to date. The two focus Callahan’s story on his alcoholism, his tragic accident (caused when Callahan’s drunk friend drove his car at 90 miles per hour into a utility pole), and his 12-step recovery. Aiding in the latter is Callahan’s sponsor Donnie, played with well-coiffed panache by a bearded, pajama-clad Jonah Hill. There is a sweetness to the film that belies the usual tastes of these three collaborators.

“This is probably one of the top two or three, if not the best, acting experiences I’ve ever had,” said Hill, with a big grin on his face. “I had experiences on this movie that were very life-changing in a lot of ways. Yeah, just creative flow.”

“Thank you, buddy,” replied Hill, before explaining why this experience was so singular. “I’m usually playing a lot of people with a lot of really fucked-up shit going on. They are usually nightmares inside. I was the happiest I ever was playing Donnie, because he had already been through most of the horrifying shit in his life, and he was on the other end of it, helping people get better. I just felt a real peace playing him, and that was really cool.”

Phoenix was charged with the challenge of portraying a man his Portland-based director knew well. “When you have a real person you’re portraying, they become very close to you,” said Van Sant. “Even if you are not actually best friends, you think of them as one, because you’re studying them. As far as I know, John might have been using me as the tool to get what he wanted. But I always felt like it was fun.”

The Callahan family had given Van Sant and company their blessing, and Phoenix spent months learning Callahan’s limited body movements—visiting the rehab where Callahan recuperated, trying to master a person beloved by many. For him, the goal was to get to a place where he didn’t need to go back to his trailer to review his notes on the scene—to get to a point where he no longer needed to rely on his preparation at all.

“No matter what the character is, the real challenge is to get to the place where you’re irreverent,” he said. “Every movie I’ve done, whether it’s fictional or not, you go, ‘This is amazing, and magical, and how do I find this?’ The best stuff is the moment where somebody’s like, ‘Oh, you forgot that line,’ and you go, ‘Whatever.’ That’s what I want to get to.”

He added, “It was really great that we had John’s blessing and his family’s blessing, but at some point you have to say, ‘This is ours.’ It’s a little scary. It can be uncomfortable, because you want to make everybody happy. But I think it’s the only way.”

Phoenix couldn’t help but look back on his first experience with Van Sant all those years ago, and how he infused the actor with a greater understanding of what an actor is supposed to do on set. “Gus made me look at the set in a different way,” said Phoenix. “I always thought you’re supposed to achieve what’s in the script. It’s a very specific goal. Gus opened it up to where there are these other possibilities that might not be in the script. There’s a way about moving around the room and utilizing props that might add another layer to it. That was such an important thing to learn at that age.”

At 65, Van Sant has become responsible for some of Hollywood’s best male performances—from Matt Dillon in Drugstore Cowboy to Joaquin’s brother, River Phoenix, in My Own Private Idaho and Robin Williams in Good Will Hunting, which nabbed the late comedian a best-supporting-actor Oscar. Phoenix credits the director with seeing an actor’s potential before the actor realizes it.

“We were doing this scene, and I was terrible. I was fucking terrible. It was the worst scene in the world. If I was a director, I’d go, like, “O.K., everybody. We’ve got a real fucking problem here. This is a disaster,” said Phoenix. “Gus kept saying, ‘Do it again.’ And then, as I went in for the last take, he said something as I was wheeling into the room, but I didn’t hear him. I did the take, and I was actually experiencing what I was saying to the other actor. I came off, and I said, ‘What did you say? I didn’t hear you.’ He said, ‘Oh, I just said you’re going to get it in this next take.’ He just knew.”

Phoenix and Hill look to Van Sant for a response. “It was a really hard scene,” he said. “So, it wasn’t awful. It was just the beginning of doing a hard scene.”